Use a mixer with beaters or the paddle attachment to beat the butter and both sugars together until light and fluffy. If you don't have an electric mixer, use a wooden spoon to ensure the sugars get dissolved in the butter.
Beat in the vanilla extract and egg, switching to a whisk if you are doing this by hand.
Place the gluten-free flour, baking powder, baking soda, and salt in the bowl. Lightly stir them together on top with a spatula, then mix until there are no dry spots. The dough will be fairly thick. Fold in the white chocolate chips and dried cranberries until evenly distributed.
Use a 3-tbsp cookie scoop to scoop the dough into 12 balls. Place on a small parchment-lined baking sheet or plate. Top each ball with a few extra chocolate chips and cranberries then refrigerate for 30 minutes. Halfway through the chill time, preheat the oven to 350ºF.
Place the dough balls on 1-2 large parchment-lined baking sheets, making sure there is room for the cookies to spread. Bake for 10-12 minutes until the edges are lightly coloured and the centres are still a little soft. For perfectly round cookies, take a large cookie cutter or the top of a glass and gently run it around each cookie immediately after removing from the oven. This will reinforce a circular shape as the cookie cools.
Allow the cookies to cool on the baking sheet for 15 minutes until they have set slightly, then transfer to a wire rack to continue cooling. Enjoy warm or allow to come to room temperature.